WT1 (Wilms' tumor gene 1) gene is a transcription regulatory factor (Call K. M. et al., Cell 60, 509–520, 1990; Gessler M. et al., Nature 343, 774–778, 1990) discovered in the course of identifying a causative gene of Wilms' tumor which is a pediatric kidney tumor, and functions as a tumor suppressor gene in at least some Wilms' tumors. It was also discovered that its level of expression is high in most leukemia cells, and it is becoming clear that its level of expression at the first medical examination for leukemia correlates well with prognosis, and it is extremely useful as a marker of minimal residual disease (MRD) of leukemia (Inoue K. et al., Blood 84, 3071–3079, 1994).
In normal tissue, WT1 is highly expressed in the testis, the ovary, the spleen, the mesenchymal mesothelium as well as in the embryonal kidney. Among malignant tumors, it is also highly expressed in leukemia, malignant mesothelioma, and solid tumors such as lung cancer. There is increasing evidence that the WT1 gene is a gene having a variety of functions in organogenesis, oncogenesis and the like (Reddy J. C. et al., Biochim. Biophys. Acta. 1287, 1–28, 1996; Davices R. et al., Cancer Res. 59, 1747–1751, 1999).
The WT1 gene is mainly translated into four proteins by alternative splicing in the exons (A in FIG. 1). The longest gene product, in which exon 5 comprising 17 amino acid residues (17AA) and three amino acid residues (KTS1) in between the third and the fourth Zinc fingers have been inserted, is designated herein as WT1(+/+).
It has been demonstrated that the KTS-containing WT1(+/+) has a weak DNA binding ability and binds to the mRNA splicing protein, whereas the WT1(+/−) having a potent DNA-binding ability functions as a transcription regulatory factor.
The WT1 protein is roughly composed of two regions, i.e., the function regulatory region and the DNA-binding region containing zinc fingers. In the function regulatory region, as shown in A in FIG. 1, have two domains that suppress or activate transcription. The assumption that proteins that bind to these regions may be responsible for the regulation of functions led to the discovery of various WT1 interacting proteins. They include various proteins such as p53 (Malheswran S. et al., Proc. Natl. Acad. Sci. USA 90, 5100–5104, 1993), ubiquitine conjugating enzyme 9 (Wany Z. Y. et al., J. Biol. Chem. 271, 24811–24816, 1996), par-4 (Johnstone R. W. et al., Mol. Cell Biol. 16, 6945–6956, 1990), U2AF65 (Ravis R. C. et al., Geves. Rev. 12, 3217–3225, 1998), and hsp70 (Maheswaran S. et al., Geves Rev. 12, 1108–1120, 1998). However, there are no reports of specific binding proteins in leukemia cells.